One of the two rolls of two-roller roll presses is frequently designed as a fixed roll, whose bearing is supported directly on the machine frame, while the second (loose roll) has force-exerting elements (hydraulic cylinders, spring constructions) between the bearings and the machine frame. These force-exerting elements generate the pressing forces and enable the loose roller to yield if the opposing force of the material to be ground exceeds the maximum pressing force. In case of a non-parallel roll gap, the loose roller will be in an oblique position and axial forces will thus develop, which must be absorbed by at least one thrust bearing in order to prevent a displacement of the roll.
Spherical roller bearings, which can also absorb axial loads, in addition to radial ones, are therefore used in the state of the art. Other embodiments in the state of the art make provisions for using, instead of spherical roller bearings, multi-row cylindrical roller bearings, but these are unable to absorb any axial forces. These cylindrical roller bearings are therefore complemented by axial supports, which absorb the axial forces. Thrust bearings are, in particular, suitable for use as a support. The conventional roll bearing thus comprises a fixed bearing, a combination of cylindrical roller bearing and self-aligning roller thrust bearing, on one side of the roll and a cylindrical roller bearing as a movable bearing, preferably on the drive side of the roll.
The thrust bearings are preferably fastened on the shaft journal by means of shrinking. The thrust bearings are heated for this purpose and will become firmly seated on the shaft journal due to the heat shrinking after cooling.
However, this form of construction proved to be disadvantageous, because the service lives and the resulting intervals between which the roll surfaces need to be replaced are markedly shorter than the intervals at which the thrust bearings need to be replaced. This means that whenever the roll bearing is removed for maintenance of the roll surface or for replacing the roll, the thrust bearing also has to be pulled off from the shaft journal thereof in a complicated procedure and pulled again over the shaft journal of the replacement roller. This problem is solved by DE 101 36 201 A1, which proposes that the thrust bearing be shrunk on the ring cap-like cover plate of the bearing rather than on the shaft. This assembly unit is then pushed, with the “outer thrust bearing cap” mounted, over the shaft journal with a slight clearance and screwed to same axially. A co-rotating ball race, which runs against non-co-rotating gasket rings and thus brings about a sealing of the roller bearing, is provided on the outer side of the cover plate.
Practical experience has shown that this thrust bearing mount construction does not meet the requirements and problems arise time and time again because of cooling water leaks at the flat packing between the assembly unit and the plane of the screw connection at the shaft journal. It is, furthermore, problematic that the outer thrust bearing cap with its ring-shaped thrust bearing housing shape projecting in breadth was manufactured as a cast part (more cost-effective than a welded part), which led to complicated production with relatively high costs. The mounting and removal of the thrust bearing is also more complicated than desired because of the large number of fitting tolerances.
In another embodiment known from the state of the art, the thrust bearing and the ball race are shrunk, due to the design, tightly onto the shaft. The one-part “outer thrust bearing cap” made of a casting is mounted in advance. For removal, e.g., in case of a roll replacement, the thrust bearings shrunk in pairs onto the shaft must be pulled off with a pulling device to be manufactured specifically for this purpose, together with the “outer thrust bearing cap,” without suitable preheating (thrust bearings are seated enclosed on three sides in the outer thrust bearing cap). This procedure is time-consuming because of the tight seating of the part and the difficulty or impossibility of heating the thrust bearings.